This invention relates to a linkage for connecting a brake cable to an actuator in a drum-in-hat park brake.
In a vehicle having four wheel disc brakes overall cost saving may be achieved through the use of a drum-in-hat parking brake such as disclosed in U.S. Pat. No. 5,180,037 as many of the structural components for a conventional service brake may be used in a parking brake. In a study of parking brakes, it was summarized that less than twenty five percent of drivers effect a parking brake application on a regular basis and the use of a parking brake was even less in vehicles having an automatic transmission. It was found that with such limited use, an initial thickness of the material of friction members for a parking brake remains essentially the same over the life of a vehicle regardless of the relative large coefficient of friction between the friction pads and drum needed to hold a vehicle stationary. Thus, it is common to develop a typical high coefficient of friction for a friction lining for a parking brake from a composition of materials mainly consisting of metal oxides, ceramic particles, carbon particles, fibers and other materials retained in a phenolic matrix. The relative limited wear is not unexpected, as a vehicle is stationary when a parking brake application is applied and as a result frictional wear normally does not occur. However, current safety standards require a park brake to also be capable of functioning as an emergency brake and have an ability to achieve a minimum of six rolling stops from a speed of 18.6 miles per hour. In order to meet this requirement, it is not uncommon for an actuation force of approximately 100 Kg must be applied to bring brake shoes into engagement with a drum.
It is not uncommon for the drum-in-hat parking brake to be assembled at one place and later installed on a vehicle in another location through a brake cable connection such as disclosed in U.S. Pat. No. 5,174,170 or U.S. patent application Ser. No. 10/171,142 filed Jun. 13, 2002 now U.S. Pat No. 6,651,789. Since it may be difficult and time consuming to install a brake cable to the actuator on an assembly line as such assembly is essentially a blind entry, it has been suggested that a stub linkage be provided with a drum-in-hat assembly the end thereof later joined to a brake cable by a crimp connection. Unfortunately the stub linkage and crimp connection can add cost of the overall brake assembly and as a result customers would prefer a different solution to this situation.
A primary object of the present invention is to provide a low cost linkage for joining a brake cable to an actuator in a drum-in-hat park brake.
According to this invention, a drum-in-hat park brake assembly for a vehicle has a first brake shoe and a second brake shoe that are respectively retained on a backing plate secured to a vehicle. The first brake shoe and the second brake shoe each have a first web with a first engagement end and a second engagement end. The first engagement end of each of the first and second webs is aligned with an anchor secured to the vehicle while the second engagement end of each of the first and second webs is spaced apart by an actuator assembly. First and second springs are attached to the first and second webs and urge the first and second webs toward the anchor and an actuator assembly. The actuator assembly upon receiving an actuation force acts on the first engagement ends to move the first and second friction members associated with the first and second brake shoes into engagement with a drum to effect a brake application. The actuator assembly is characterized by a housing with a first end that engages the first web and a second end that engages the second web and a lever that is pivotally retained in the housing. The lever has a first end that engages the first web and a second end with a hook thereon that is connected to an actuation cable by a linkage that is formed from a substantially continuous wire. The linkage is defined a base with parallel and adjacent first and second legs that are located in a first plane perpendicular to the base and parallel and adjacent third and fourth legs that are located in a second plane perpendicular to the base. The first and second legs each have a first section that extend a first distance from the base to a first loop and a second section that extend a second distance from the first loop to a second loop while the third and fourth legs each extend a third distance from the base. The base has an opening defined by a complementary shape between the first leg and the third leg and the second leg and the fourth leg. The base receives a head member on a cable after the head passes through the first loop and a force is applied to the cable to expand the first section and allow the cable to be located in the opening and the head to be positioned between the first and second legs and the third and fourth legs. An actuation force is communicated through the head and communicated through the first and second legs by the second loop pulling on the lever to move the first and second brake pads into engagement with a drum and effect a brake application.
An advantage of this invention resides in a simple wire formed linkage for joining a brake cable with a lever in an actuator for a drum-in-hat brake assembly.